Manufacturing processes utilizing deposition techniques have been developed for rapid prototyping of three-dimensional parts and tooling. For example, in U.S. Pat. No.'s 5,301,863, 5,301,415, 5,207,371 and 5,286,573 to Prinz et al., conventional systems and methods are disclosed for manufacturing three-dimensional objects by forming using thermal spray or weld deposition techniques to deposit material layers on a work surface. See also U.S. Pat. No. 5,266,098 to Chun et al.
Drop generators have also been developed and applied to the rapid prototyping of three-dimensional objects. See P. F. Jacobs, Rapid Prototyping and Manufacturing, ch. 16 (Society of Manufacturing Engineers 1992). In a conventional drop generator of this type, molten metal is ejected as a uniform laminar liquid jet from a circular injector or nozzle located at the bottom of a heated reservoir. The liquid jet is then broken into a series of uniformly sized drops by using a fixed diameter injector and an applied oscillation force near the injector or nozzle orifice. The uniformly sized drops are then deposited in layers on a substrate surface where they solidify to form the desired three-dimensional metal product.
With such techniques, resulting metal products can be designed to have fine, equiaxed micro-structures without manufacturing defects such as porosity or alloy segregation. See C.-A. Chen, P. Acquaviva, J.-H. Chun and T. Ando, “Effects of Droplet Thermal State on Deposit Microstructure in Spray Forming,” Scripta Materiala, vol. 34, pp. 689-696 (1996); J.-H. Chun and T. Ando, “Thermal Modeling of Deposit Solidification in Uniform Droplet Spray Forming,” Proceedings of the 1996 NSF Design and Manufacturing Grantees Conference, pp. 353-354 (Society of Manufacturing Engineers 1996). Other conventional systems, such as disclosed by Sterrett et al. in U.S. Pat. No. 5,617,911, use electromagnetic fields to control the deposition of uniform size drops.
The manufacturing capabilities of conventional drop generators, however, remain limited by the relatively small range of possible drop sizes. Greater variability in the drop size is desired to allow more efficient rapid prototyping by allowing the mass flux to be set according to the outline geometry and desired internal micro-structure of the product at a given point. Despite the variability of external oscillation, the possible range of drop sizes from a conventional drop generator is limited by the fixed injector diameter, which is typically less than one millimeter.